Systems that convert between kinetic energy and electrical energy, such as free piston systems, sometimes require fault management. Typical mechanically linked systems provide for a fixed trajectory. For example, in a conventional piston engine, energy is transferred to a crankshaft during an expansion stroke, while it is removed from the crankshaft during a compression stroke. If a fault occurs, the trajectory is usually maintained, and the moving parts can effectively spool down to a stop safely and predictably. Systems that do not include mechanical constraints, such as a free-piston machines having linear motors, for example, conventionally rely on extensive real-time control, and the loss of that control can be catastrophic.
Systems having multiple piston assemblies, such as opposed-piston engines typically require that the assemblies remain synchronized to some extent. If aspects of control are lost, or other faults occur, synchronization may suffer, and behavior of the system might become unpredictable.